A railcar generally provides a pair of side frames on each side having downwardly opening jaws. A bearing adapter is vertically moveable within the jaw and rests on a bearing mounted on a railcar axle carrying a wheel of the railcar. The bearing adapter is thus a rigid connection between the bogie frame of the railcar and the bearing. Typically, a bearing for a railcar axle fits around a journal at the end of the railcar axle where it is mounted between a backing ring assembly and an end cap.
Due to limited bearing support surface, the load applied on the bearing by the railcar adapter is not well distributed on the bearing, notably on the rolling elements when the bearing is of the rolling bearing type. This results in wear on the inner surface and the outer surface of the railcar adapter, as well as in failure of the bearing.
In order to improve the load distribution on the bearing, the outer surface of the railcar adapters is provided with a central groove extending in an axis parallel to the bearing rotational axis.